The 3d 2D5⁄2 - 2D3⁄2 magnetic dipole transition in potassium-like ions

Spectral lines of the magnetic-dipole transition between the <?CDATA 3d ²D3/2,\, 5/2?> 3 d 2 D 3 / 2 , 5 / 2 levels of K-like Kr 17+ , Zr 21+ , Nb 22+ , Mo 23+ , and Ru 25+ ions were measured in a compact electron beam ion trap. By means of dedicated calibration methods, the transition wavelengths of Kr 17+ , Zr 21+ , and Mo 23+ ions reduce uncertainties by at least one order of magnitude and the wavelengths of Nb 22+ and Ru 25+ ions are measured for the first time at a few ppm level. In addition, the fine-structure energy splittings were systematically calculated using the multiconfiguration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach. The contributions of the core-valence and core-core electron correlations, the Breit interaction and QED effect were discussed in detail. The results show that it is essential to include deep core-valence correlation of L -shell and core-core valence correlation of 3 p subshell to obtain an agreement better than 0.15% with existing experimental values. The calculation model can be performed to predict the wavelength within a high accuracy for a wide range of potassium-like ions.